Phenylephrine (Neo-Synephrine®), (R)-3-(1-hydroxy-2-methylamino-ethyl)-phenol, is an orally and intravenously administered putative agonist of the alpha adrenergic receptor (α1-selective). Phenylephrine is available over the counter as a nasal decongestant. Phenylephrine can also effectively treat hypotension (Rose et al., Neurocritical Care 2004, 1(3), 287-299), and is used frequently in intensive care units to maintain adequate tension in patients. Phenylephrine is not inotropic or chronotropic, it elevates the blood pressure without increasing the heart rate or contractility. Phenylephrine can also treat migraines (Willems et al., Drug News & Perspectives 2002, 15(3), 140-146) and ischemic heart disease (Cohen et al., Annual Review of Medicine 1996, 47, 21-29).

The chemical structure of phenylephrine contains a number of positions that are susceptible to action by metabolic enzymes. For example, the N-methyl group can be oxidized which could then lead to a norepinephrine-like structure, if coupled with an appropriate aromatic hydroxylation. The methylene group alpha to the nitrogen is likely to oxidized, since the hydroxymandelic acid metabolite accounts for more than 50% of the recovered mass balance. Monoamine oxidase (MAO) is responsible for much of the clearance.